Various systems for transferring ink images onto a substrate, such as a fabric or an article of manufacture, are known. For example, images can be transferred from a heat transfer sheet by the use of heat and pressure. Such sheets (also known as hot-stamp foils) are shown, for example, U.S. Pat. No. 5,124,309, to Egashira, and U.S. Pat. No. 5,223,476, to Kanto et al.
More complex systems for transferring images are shown, for example, in U.S. Pat. No. 5,244,524, to Yamane. Yamane describes an ink image forming step in which an ink image is formed on a hot melting type adhesive layer of a transfer sheet, followed by an image retransferring step in which the ink image and the hot melting type adhesive layer are transferred onto the substrate by application of heat and pressure.
Various inks and dyes have been employed in known heat transfer shear or hot-stamp foils. For certain applications, it would be desirable to employ a so-called thermochromic compound, that is, a compound which changes color (typically from colored to colorless or vice versa) at a specified transition temperature. Images so formed can, for example, provide an indication of the temperature of the substrate to which they are applied, or can provide a decorative effect.
It would be desirable to provide an improved hot-stamp foil comprising a layer which includes a thermochromic compound, and preferably a thermochromic layer which provides a reversible thermochromic effect.